7. Add Fencing to Cluster

Fencing is the disconnection of a node from shared storage. Fencing cuts off I/O from shared storage, thus ensuring data integrity.

A fence device is a hardware device that can be used to cut a node off from shared storage.

This can be accomplished in a variety of ways: powering off the node via a remote power switch, disabling a Fiber Channel switch port, or revoking a host’s SCSI 3 reservations.

A fence agent is a software program that connects to a fence device in order to ask the fence device to cut off access to a node’s shared storage (via powering off the node or removing access to the shared storage by other means).

9. Types of Failover Domain

A failover domain is an ordered subset of cluster members to which a resource group or service may be bound.

The following are the different types of failover domains:

Restricted failover-domain: Resource groups or service bound to the domain may only run on cluster members which are also members of the failover domain. If no members of failover domain are availables, the resource group or service is placed in stopped state.

Unrestricted failover-domain: Resource groups bound to this domain may run on all cluster members, but will run on a member of the domain whenever one is available. This means that if a resource group is running outside of the domain and member of the domain transitions online, the resource group or

service will migrate to that cluster member.

Ordered domain: Nodes in the ordered domain are assigned a priority level from 1-100. Priority 1 being highest and 100 being the lowest. A node with the highest priority will run the resource group. The resource if it was running on node 2, will migrate to node 1 when it becomes online.

Unordered domain: Members of the domain have no order of preference. Any member may run in the resource group. Resource group will always migrate to members of their failover domain whenever possible.

10. Add a Filover Domain

To add a failover domain, execute the following command. In this example, I created domain named as “webserverdomain”,

[root@rh1 ~]# ccs -h rh1 --addfailoverdomain webserverdomain ordered

Once the failover domain is created, add both the nodes to the failover domain as shown below:

11. Add Resources to Cluster

Now it is time to add a resources. This indicates the services that also should failover along with ip and filesystem when a node fails. For example, the Apache webserver can be part of the failover in the Redhat Linux Cluster.

When you are ready to add resources, there are 2 ways you can do this.

You can add as global resources or add a resource directly to resource group or service.

The advantage of adding it as global resource is that if you want to add the resource to more than one service group you can just reference the global resource on your service or resource group.

In this example, we added the filesystem on a shared storage as global resource and referenced it on the service.